Electric discharge device



Jan. 10-, 1961 H. E. zuvERs 2,967,966

ELECTRIC DISCHARGE DEVICE Filed April 26, 1960 INVENTOR: HOWARD E. ZUVERS,

HIS ATTORNEY.

United States atent O ELECTRIC DISCHARGE DEVICE Howard E. Zuvers, Scotia, N.Y., assignor to General Electric Company, a corporation of New York Filed Apr. 26, 1960, Ser. No. 24,692

5 Claims. (Cl. 313-161) My invention relates to electric discharge devices and pertains more particularly to an improved electric are dis charge device of the pool-cathode type.

Electric arc discharge devices of the type including an anode, a liquid metal pool cathode and means for initiating an arc discharge between the anode and cathode are well known. The devices are characterized by unilateral current conduction between the anode and cathode and have been widely used for the controlled transfer of current of large magnitudes from one operating circuit to another.

Heretofore, in some installations of devices of the above-described type, considerable difliculties have been experienced by failure of the devices to maintain their unilateral conductive characteristics. As recognized by Burnice D. Bedford in his U.S. Patent 2,634,382, issued April 7, 1953, and assigned to the same assignee as the present invention, the mentioned failure is often attributable to the formation of cathode spots on portions of the discharge device other than the pool cathode and caused by unsymmetrical magnetic fields within the discharge space. As also recognized by Bedford the unsymmetrical magnetic fields can be caused by current in external circuits connected with the discharge path.

Structure disclosed and claimed in the mentioned Bedford patent, and whereby the mentioned difiiculty can be effectively overcome, involves the provision of a conductive structure surrounding the tube envelope and coniductively connected to the cathode for conducting the tube current externally of the tube in a uniform manner with respect to the tube axis. This structure serves to eliminate the above-discussed difficulti s.

In some applications of pool cathode devices of the described type such, for example, as in certain welding circuits and fusion-research control circuitry, the devices are required to switch extremely high currents at high voltages. Under such conditions of operation the presence of a magnetic field other than that produced by the inter-electrode current can result in the aforementioned difliculties and, therefore, it becomes increasingly important that such a field not be present in the region between the anode and cathode. In an effort to insure uniform circumferential distribution of returning tube current and thus insure against the presence of such other undesired magnetic fields in the arc region, the conductive wall of the envelope of the device has been utilized as part of the tube circuit. Additionally, a low-resistance conductive ring fitted with a laterally-extending cathode connector has been mounted about the upper end of the tube wall in an effort to insure uniform concentric distribution of the tube current. However, at certain extremely high current and voltage conditions it is still possible with this form of structure for the current to become non-uniformly distributed in the current path and thus result in the presence of an unsymmetrical magnetic field in the device which may subject the device to the same A type of difiiculty encountered before recognition of the basic problem by Bedford.

Further, I have recognized that when the discharge are is maintained centered in the device, more effective utilization is made of the opposed electrode surfaces, the arc is enabled to operate hotter, and desirable uniformly lower arc drop over a wide current range and greater operating efiiciency result. Specifically, when the arc is maintained centered more of it runs to the liquid cathode rather than to the envelope side wall, resulting in greater are current conduction. Additionally, in tubes of this type the side walls of the envelope are usually cooled and by keeping the are centered, and thus relatively remote from the cooler side walls, are losses are minimized, contributing to the lower arc drop.

My invention contemplates the provision of means effective for insuring uniform circumferential distribution of the returning tube current and thereby maintaining desired centering of the discharge are at substantially all values of current and voltage. To this end, I provide a pool-cathode electric discharge device including a cylindrical conductive wall conductively contacted by the cathode pool and extending about the device upward toward the anode. Bonded to the anode end of the wall is'coaxial combined mounting flange and electrical contact. The Wall and contact are both formed of a material of predetermined electrical resistance, whereby the current from the cathode is force-paralleled through the wall and coaxial contact for insuring uniform distribution of the current circumferentially about the device regardless of the current and voltage requirements placed on the device. Thus, my arrangement insures against the presence of unsymmetrical magnetic fields in the discharge space and maintains the arc centered in the device. Additionally, my arrangement facilitates both manufacture of the device and mounting thereof in equipment.

Accordingly, a primary object of my invention is to provide a new and improved arc discharge device of the pool-cathode type adapted for uniformly low arc drop and resultant greater operating efliciency over a substantially wide high current range.

Another object of my invention is to provide a new and improved are discharge device of the pool-cathode type including improved means for insuring a magnetic fieldfree arc region therein.

Another object of my invention is to provide a new and improved arc discharge device including improved means for providing both a uniform coaxial cathode connection and facilitating mounting of the device in equipment.

Still another object of my invention is to provide an improved electric discharge device envelope structure adapted for insuring a uniformly magnetic field-free arc region between the anode and cathode thereof regardless of current requirements placed on the tube and in a manner which is substantially simpler than prior art structures from both the structural and manufacturing standpoints.

Further objects and advantages of my invention will become apparent as the following description proceeds and the features of novelty which characterize my invention will be pointed out with particularity in the claims annexed to and forming part of this specification.

In carrying out the objects of my invention I provide an arc discharge device comprising an envelope containing an anode and a mercury pool cathode in mutually spaced relation. The envelope includes spaced inner and outer walls defining a coolant passage and at least the outer wall comprises a cylinder formed of a high electrical resistance ferrous material which extends the full length of the envelope and is electrically contacted by the cathode. To the rim of the upper end of the cylinder is circumferen- 3 tially welded theinner rimof'a combined coaxial cathode contact and mounting flange formed of the same material as the cylinder.

For abetter understanding of my invention, reference may be had to the accompanying drawing in'which:

Figure lis a partially sectionalized elevational'view of anarc discharge device incorporating an embodiment of my invention;

Figure 2 is a planview of the device illustrated in Figure 1; and

Figure 3 is a plan'view of a modified form of my inventlon.

Referring to the drawing, there is shown in Figure 1 an arc discharge device constructed according toan embodiment of my invention and generally designated 1. The device'l includes a generally cylindrical metal envelope 2 comprising spaced inner and outer walls 3and 4, respectively, defining a coolant circulating chamber. Additionally, the envelope includes upper and lower header constructions 5 and 6, respectively. The coolant chamber is provided with coolant inlet and outlet connectors 7 and8, respectively.

Contained in the lower end of the envelope is a liquidous cathode it} which can'comprise a pool of mercury. Alternatively, the cathode it) can be formed of a mixture of liquid cathode pool materials or can comprise one of the well known sponge-type cathodes which are constituted of a porous member imbued with an active liquid cathode material.

Suitably sealed and supported in the upper header 5 in axially spaced and insulated relation with respect to the cathode 10 is an anode 11 which is coaxially located with respect to the envelope and cathode. Connected to the anode in a suitable electrically conductive manner is an external anode terminal 12. Also provided in the envelope is an arc initiating element13 which is adapted for initiating operation of the device in a well-known manner.

While I have shown in Figure 1 a device incorporating only 2 opposed electrodes namely an anode and a cathode, it is to be understood from the outset that the present invention is equally applicable to structures incorporating other electrodes such, for example, as one or more grid electrodes interposed between the anode and cathode.

In accordance with my invention the bottom of the metal envelope is electrically contacted by the pool cathode, and at least the outer wall 4 of the envelope is formed of a high electrical resistance ferrous material having a resistance preferably in the range of from approximately 7 to 20 microhm-cm. and which can advantageously comprise stainless or mild steel. To the upper rim of the outer wall member is circumferentially welded the inner rim of a coaxial planar or plate-like member 14 which is preferably formed of the same material as the envelope wall and is effective for serving as both a mounting flange and a coaxial electrical contact for the cathode. Additionally, the member 14 extends completely about and makes equal electrical connection with all circumferential portions of the upper end of the high electrical resistance envelope wall.

As seen in Figure 2, the contact member 14 can be substantially rectangular or oblong in configuration al lowing for the location therein, and preferably on the major thereof, of mounting bolt apertures 15 without subtracting from the fully circumferential nature of the connection of the member 14 to the envelope wall, or in other words, without affecting the provision of high resistance conductive material between the outer wall of the envelope and all edges of the contact member 14. The contact member 14 is adapted for engaging a combined coaxial electrical contact and support member of the type generally designated 16 and shown in dash lines in Figure land can be held in place by mounting bolts also shown in dash lines. The illustrated contact and support member would be provided in equipment incorporating the tube'as a component part thereof.

Illustrated in Figure 3 is a'modified'form of my invention wherein the coaxial contact member comprises a circular plate 17 having the inner edge thereof welded circumferentially to the upper end of the outer wall 4 of the envelope 2.. The member 17 can also be advantageously formed of a stainless or mild steel to afford the desired high electrical resistance. Additionally, the member 17 can include any number of circumferentially spaced mounting bolt apertures 18 while still affording a substantial amount of high resistance conductive material between the envelope wall and outer edge of the member.

By providing a completely coaxial cathode contact at the upper end of the envelope and by forming both the contact and at least the outer wall of the envelope of a high electrical resistance material, such as stainless or mild steel, I insure the provision of a circumferentially uniform concentric return current flow from the cathode at the bottom of the tube to the engaging contact 16 of the equipment employing the tube. This arrangement insures eircumferentially uniform current flow distribution due to the uniform electrical resistance nature of the complete circumferential current path through the envelope wall and coaxial contact 14. The particular resistance of this path which is provided by the equivalent of an infinite number of parallel resistors forces parallelism of all of the possible discrete current paths from the cathode to the equipment contact 16, regardless of the amount of current flowing therethrough. As a result, the current flowing from the cathode to the equipment contact 16 is maintained circumferentially uniform, regardless of the high current requirements that may be placed on the device, such as in welding apparatus. Thus the device is assuredly protected against the presence therein of unsymmetrical magnetic fields which can adversely affect the operation of the device. Expressed inanother manner, regardless of the load requirement placed on the device my invention insures against unsymmetrical return of current flow through the wall of the device, completely from the cathode to the contact 26 and thus insures against the presence in the device of undesired magnetic fields which can adversely affect tube operation. The absence of such undesired fields insures centering of the arc in the device. This results in greater effective utilization of the opposed active electrode surfaces and keeps the are remote from the cooler envelope side walls, which, in turn, enables higher current conduction at given ratings and uniformly lower arc drop over a wide current range which can he as much as 10 to 20 times the normal current rating for a device. Expressed in another manner, my arrangement so insures centering of the are that the device can be operated at current levels 10 to 20 times higherthan its normal rating before arcing to the side walls occurs and before the mentioned uniformity of voltage drop and the desired advantage of lower voltage drops will be lost.

in addition to the above-discussed insurance of a circumferentially unirorm current return path, my structure affords ease of mounting the tube. Further, my structure provides both these advantages and yet is structurally simpler than those devices found in the prior art. This simplicity of structure also greatly facilitates manufacture since, from the manufacturing standpoint, it involves simply the circumferential welding of the coaxial contact to the outer cylinder and, further, since the welding required is between members which can both be formed of stainless or mild steels which are readily weldable. Still further, inasmuch as the coaxial contact in my structure serves as both a coaxial contact and a mounting flange, my invention obviates the need for providing separate cathode connectors and tube mounting means on the envelope.

While I have shown and described specific embodiments of my invention, I do not desire my invention to be limited to the particular forms shown and described, and I intend by the appended claims to cover all modifications within the spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. An arc discharge device comprising a generally cylindrical metal envelope, a liquidous cathode within said envelope at one end thereof and electrically contacted by the lower end of the wall of said envelope, an anode supported within said envelope in axially spaced and insulated relation with respect to said cathode, a coaxial contact member circumferentially welded to the wall of said envelope above said anode, and the wall of said envelope and said coaxial contact both being formed of high electrical resistance materials, whereby circumferentially uniform current conduction about said device from said cathode to means engaged by said coaxial contact member is insured, thereby to insure against presence of undesirable magnetic fields in said device.

2. An arc discharge device according to claim 1, wherein said envelope wall and said coaxial contact member are formed of a conductive material having an electrical resistance in the range of from approximately 7 to 20 microhm-cm.

3. An arc discharge device comprising a generally cylindrical envelope including spaced inner and outer cylindrical walls defining a coolant chamber, a pool cathode within said envelope at one end thereof and electrically contacted by the lower end of said envelope, and anode supported coaxially Within said envelope in spaced and insulated relation with respect to said cathode, a coaxial combined mounting flange and contact comprising a centrally apertured plate extending transverse the longitudinal axis of said envelope and having the edge of the aperture therein circumferentially welded to the upper rim of said outer wall and at least a pair of diametrically opposed hold-down bolt apertures, and said walls and plate being formed of high electrical resistance materials, whereby circumferentially uniform current conduction about said device from said cathode and through said wall and said coaxial contact member is insured for insuring against the presence of undesired magnetic field in said envelope.

4. An electric discharge device according to claim 3, wherein said high resistance material is selected from the group consisting of stainless steel and mild steel, said coaxial contact has a generally oblong configuration, is dimensioned for alfording a substantially uniform high resistance current path therethrough completely about said envelope, and said apertures are located on the major axis of said contact.

5. An electric discharge device according to claim 3, wherein said high resistance material is selected from the group consisting of stainless steel and mild steel, said coaxial contact is circular, is dimensioned for affording a substantially uniform high resistance current path therethrough completely about said envelope, and said apertures are circumferentially spaced equally about said envelope.

References Cited in the file of this patent UNITED STATES PATENTS 2,634,382 Bedford Apr. 7, 1953 

